This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 100 64 227.6, filed on Dec. 22, 2000, the entire disclosure of which is incorporated herein by reference.
The invention relates to an arrangement for coupling or connecting two double-walled pipes to each other. The double-walled pipes may especially be for conveying a liquid therein, such as fuel in an aircraft.
In various special applications, it has long been necessary to provide a high degree of safety and reliability of a pipe for conveying fluids therein. For example, in aircraft construction, such requirements apply to fuel lines, for which double-walled pipes including an inner pipe surrounded by an outer pipe have typically been used. It is also necessary to provide reliable trouble-free liquid-tight joints or connections of segments of the double-walled pipe to each other. Thereby, the double-walled pipe, such as a fuel line, can be rationally installed and maintained. In the event that seal elements included in the connections of these double-walled pipe segments lose their sealing ability over time, it must be possible to disassemble the pipe connection easily to allow the seal elements to be exchanged in an uncomplicated and economical manner. Moreover, it is necessary that the connection provides easy accessibility to the double-walled pipes for prophylactic inspection and maintenance, often in rather tight installation spaces. As a further requirement, especially in the context of aircraft fuel lines, the pipe connections must be electrically connected to a metal structure such as the aircraft airframe to provide an electrical conduction path, and especially a grounding path, and there must be no danger of an electrical line interruption between the pipe connection and the metal structure. Furthermore, it should not be necessary to carry out a repeated mechanical positioning, alignment or orientation of the double-walled pipe segments or the connection thereof, after carrying out any required maintenance procedures.
Connection arrangements for double-walled pipes of the above described general type are used, for example, in the trim tank fuel lines for modern aircraft such as the Airbus A300, A310, A330 and A340 aircraft. Such conventional trim tank fuel line connections, as shown in present FIGS. 1 and 2, will be described in detail below. While such a pipe connection has many benefits and advantages, it has also been found to suffer certain disadvantages in the context of installation and maintenance thereof. It is considered that the installation and maintenance requirements can be improved, because they have not been improved or economized, but rather have stayed essentially unchanged, over a long time span.
Due to the typical rather tight installation spaces for the trim tank fuel lines in an aircraft, it is difficult and inconvenient to access the fuel line installation for the purpose of inspection and maintenance. This makes it difficult to replace the seal elements of the conventional pipe connections in the event that the seal elements lose their sealing properties over time, for example due to the effects of aging of the seal material. Thus, improved accessibility for the purpose of maintenance and prophylactic inspection of the double-walled fuel lines and their connections is a highly desirable improvement.
Also, the conventional pipe connections do not reliably ensure that a constant electrical connection between the pipe line arrangement and the aircraft structure will be maintained at all times while carrying out maintenance procedures. This is necessary for continuously maintaining protection against lightning strikes and the like. Especially when carrying out a seal element exchange, which requires opening and disassembling the pipe connection, this procedure results in interrupting the electrical conduction path. Furthermore, with the conventional pipe connections, it is generally necessary to carry out a renewed positioning, aligning, or orienting of the pipe connection and the pipe segments after the maintenance work has been completed and the connection has been reassembled.
In view of the above, it is an object of the invention to provide an arrangement for connecting two double-walled pipes, which is improved in such a manner so that such pipes can be easily and rationally installed along a straight pipeline path, especially in an aircraft, and which allows all installed seal elements to be exchanged in an uncomplicated manner in the event of leakage thereof. The invention also aims to provide an improved accessibility to the double-walled pipe installation and especially the connection thereof, for the purpose of prophylactic inspection and maintenance in tight installation spaces. Another object is to ensure that an electrical connection between the arrangement and the aircraft structure will be continuously maintained while carrying out maintenance procedures, e.g. to provide continuous lightning strike protection, and to avoid the need of re-positioning and re-aligning the pipe connection after completion of any maintenance work. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in an arrangement for connecting a first double-walled pipe to a second double-walled pipe. The first double-walled pipe includes a first inner pipe surrounded, especially cylindrically coaxially surrounded, by a first outer pipe. The second double-walled pipe includes a second inner pipe surrounded, and especially cylindrically coaxially surrounded, by a second outer pipe. The pipes extend longitudinally along a longitudinal pipe axis. The ends of the first and second inner pipes are coupled with each other. A first outer pipe connection member or sleeve-shaped outer pipe flange is arranged axially movably around the first inner pipe (axially between the ends of the first outer pipe and the first inner pipe), and a second outer pipe connection member or sleeve is arranged axially movably around the second inner pipe and/or the second outer pipe. The sleeve-shaped first outer pipe flange and the second outer pipe sleeve are coupled and sealed to each other, preferably by a plug-in connection without mechanical fasteners such as bolts.
A securing fixture. e.g. including a fixing or securing body, is arranged on the outer surface of the first inner pipe, under or within the sleeve-shaped outer pipe flange. At least one threaded recess or blind hole is provided in the securing body, and extends with its hole axis along or parallel to a radial line extending radially relative to the longitudinal pipe axis. For example, the securing body may be a solid generally rectangular or parallelepiped block having an arched or saddle-shaped base surface with a contour that matches and is seated on the cylindrical outer surface of the first inner pipe, and having a flat planar top surface with the at least one threaded recess or blind hole therein.
At least one throughhole is provided in the sleeve-shaped first outer pipe flange, in alignment with the at least one threaded recess or blind hole in the securing body, in an assembled condition of the pipe connection arrangement. At least one threaded screw or bolt extends through the respective throughhole and is secured in the threaded recess or blind hole in the securing body, in the assembled condition of the pipe connection arrangement. The at least one screw extends along or parallel to a radial line extending radially relative to the longitudinal axis of the pipe. The term xe2x80x9cscrewxe2x80x9d herein refers to all types of threaded fasteners. The sleeve-shaped first outer pipe flange may have a flat planar surface on one side on the outer surface thereof, through which the least one throughhole is provided, and further, a grounding connection point or lug connected thereto.